


various sins

by the_skelliest_of_sins



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Begging, Monster Heat, Other, Predator/Prey, Reader-Insert, Smut, Underfell Sans, ambiguous reader, aphrodisiacs in the venom, lamia sex, snake/little mouse, valentine's day fic
Language: English
Status: In-Progress
Published: 2018-02-15
Updated: 2018-02-20
Packaged: 2019-03-18 18:34:46
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,069
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13687431
Author URL: https://archiveofourown.org/users/the_skelliest_of_sins/pseuds/the_skelliest_of_sins
Summary: as the title suggests, this is just the various sins i write





	1. Red's Valentine's Day

**Author's Note:**

> you come home and can't find Red, he said he was sick so he stayed home to plan something but "something" came up~

“Red, I'm ho-” you start as you walk through the door, not seeing him on the couch waiting for you. ‘Huh, that's weird’ you thought as you placed your keys on the table in the little bowl, taking off your shoes and walking into the kitchen to get a drink.

He had today off because he said he was “sick”, meaning he called in pretending to be sick. You asked him what was wrong but he told you it was “a secret n you’d find out when ya got home”...he’s such a goob when it comes to him getting sick. ‘Whatever, i’m gonna go look for him’ you think as you grab a bottle of water from the fridge and walk around the house, searching for your lover.

You can't seem to find him anywhere, until you walk past your shared bedroom, hearing soft grunts and growls. You grow curious and knock softly on the door. “Red, is that you? Are you ok in there?” you call softly, hearing a loud growl from inside the room which sends a shiver through you. His footsteps get closer to the door and he swings it open, revealing your lover very disheveled and blushing.

“What took ya so long?” he growls, pulling you into the room and slamming the door closed, pressing you against it a little roughly. He presses himself into you, growling in your ear. “I planned ta make a romantic night but...fuckin heat...god i couldn’t stop thinkin’ ‘bout fuckin ya senseless…” With his words he’s grinding his obvious erection into your thigh, hands pulling at your work clothes desperately. 

You gasp at his hurriedness, trying to push him back slightly so you can breathe. He growls even deeper in pitch, pressing harder into you. “Doll...i know this ain’t a romantic thing but i need this...i need ta feel ya squirmin’ under me as i pound ya inta th’ bed...please? Please baby, i need this so bad...I-i haven't came at all, n it’s startin’ ta hurt…” his expression changes slightly, morphing from dominating and angular to pleading and soft, eyelights desperate.

You hum softly, pulling his face to yours and kissing him deeply and passionately as you grind your thigh up against his crotch as an answer. He moans softly before grabbing your hips, ripping your pants off and-quite literally-throwing you onto the bed, which has rose petals half-hazardly strewn across it in an attempt at romance. You giggle softly, it turns into a moan at the end as he spreads your legs apart, wiggling between them and leaning over your form, his excitement pressing against you throbbing with need. You mewl softly and attempt to grind down against it. 

“Please...Red please don’t hold back...i don’t want you to be uncomfortable anymore~” you tease, gripping his ribs and pulling him closer as you wrap your legs around his waist. He growls and shivers, moving a hand from your hips to his cock to guide it inside you, thrusting all the way in immediately, ripping a moan from your lungs as he groans and huffs. He gives you a few seconds to adjust before starting a fast and hard pace, which turns you into a panting, mewling, and moaning mess. He only takes that as a challenge, growling and moaning as he moves a leg up to his shoulder, thrusting deeper and harder. “H-haaaa...R-red please i-i...oh fuck please~” you whimper, arching into him and clawing at his bones. 

“F-fuck...and i thought I needed this...if ya really want it...then here ya go!” he growls as he thrusts harder, moaning loudly as his cock twitches with his impending orgasm. You’re not too far behind him, already feeling your gut twitch and quiver with the beginning signs of your release. On a particularly deep thrust he rams against your sensitive spot, causing you to scream loudly, cumming hard as he continuously rams you. Your voice is hoarse as you whimper and mewl overstimulated. Red looks down at you and drools a little at your lewd expression, shivering as he thrusts as deep as possible into you, filling you with his seed as he leans down, kissing you deeply.

The sounds of your and Red’s panting and soft mewling fill the room. You close your eyes and pant hard, trying to calm your breathing a little. Red looks down at you, his cock twitching inside you as he gets hard again. You whine and peak up at him, seeing his grin wide and animalistic. “What? Didja think i’d be satisfied afta jus one round~? Oh no, Doll, i got a lot more in me, think ya can handle it?” he teases, thrusting into you a little. You whimper softly and grin up at him. “O-oh please, you’re worried already? I’m starting to think you’re the one who can’t handle it~” 

He growls and pulls you up by your hair. “Oooh you’re gonna get it...get ready Doll…” he shifts position slightly, to where you’re on your knees and he’s behind you, cock pressing against you. He grabs your hair and pulls you back slightly, growling in your ear, which makes you more excited.

“Get ready Doll, I ain’t stoppin’ til one of us passes out…” he thrusts back in, growling. “Also, heh...Happy Valentine’s Day~”


	2. Cuddles sometimes lead to sex (lamia!Mutt x fem!reader)

**Summary for the Chapter:**

> your mate is worried about hurting you during cuddles in your shared nest, but you assure him you'll be fine. that is, until you realize what he has in store for you~

“Baaaaaabe, come back to the neeeest~” you whine to your mate, who keeps sliding around your apartment in a slight panic. “Cmon, it's fine Mutt, I promise just come cuddle...please?” 

He's currently in heat and really doesn't want to hurt you, but you keep insisting that you'll be fine. He stops his nervous wiggling and looks at you, face a slight burnt orange. “Alright...if ya promise to tell me to stop if ya don’t like it…” he mumbles, slithering into the nest and wiggling up behind you, arms around your waist. You hum happily, wiggling back into his warm embrace. He flinches slightly and tightens his grip a little, burying his face in your neck and shoulder.

“Wow, Sugarscales, you changed your mind pretty quickly~” you tease, nuzzling your cheek into his skull. He shudders slightly, trying to hold himself back, but with your ass so close...he shakes his head and grumbles into your neck, nuzzling into it more to hide his dark blushed face. You giggle and move a hand to caress his skull, rubbing circles into the back of it like you know he likes.

Small happy grumbles rumble against your bare back as he nips lovingly at your skin, making you giggle more. He growls softly and bites with a little more intensity, making your giggles turn into squeaky moans. “A-ah...Mutt…” you pant softly, unable to stop yourself from turning your head at his touch. He snaps out of it and removes his mouth from your skin. 

“Ah shit, ’m sorry I just...r-really want ta hear yer sounds…” he whines softly, tail thumping against the bed softly. You whine as he pulls back, wiggling back to press against him more. “N-no...please babe...keep going.” 

His sockets widen slightly at your words, hands rubbing circles into your clothed hips, the only thing separating his boney hands and your soft skin a pair of underwear he’s so desperately wanting to rip off you. He refrains though, even though he's in heat and wants this just as desperately as you he still wants to tease. He rubs his hand down your thigh, gently scraping his claws down the soft flesh.

“Haa…~.” you squeak, gripping onto the blankets bundled into your nest and wiggling your hips against him. “P-please~.” His sockets narrow slightly in amusement as his tail curls up around you, the tip of it tracing your nude breasts and tummy lightly, curling around your nipples before moving down. You sigh pleasurably and try to turn to face him, but his grip on your thigh tightens slightly.

“Stay…” he hisses in your ear, long forked tongue flicking out to trace your earlobe. You shiver, you love when he gets like this, loving but still dominant...it gives you the shivers thinking about it. His clawed hand traces up your thigh, caressing your hip as he nibbles on the sensitive skin of your shoulder, his other hand snaking around your waist to fondle one of your tits. You moan and writhe under his touches, wanting more but scared if you beg he’ll stop. 

“Ya like it when I tease ya, hm?” Mutt grumbles against your neck and shoulder, his rough fingers rubbing and pinching your nipple while his lower hand moves to cup your heat through your panties. You gasp and jerk your hips into his hand, arching your back. “Y-yes...oh stars I love it~” you mewl, trying to move a hand down to his tail only to have your arms restrained behind your back by a dull orange glow of magic. 

“I don't think so...yer gonna lay here n let me do what I want to ya…’s that alright, Sugar?” he hisses in your ear, nibbling it with his fangs gently. You take in a sharp breath and shudder, grinding your hips back against your scaley lover. “Oh stars yes...please Mutt, d-do what you want~” you beg, looking back at him desperately. He hisses in satisfaction as his tail slides down your belly to your panties, rubbing you through them. You gasp and whine, bucking your hips gently against his tail.

Mutt hums against your skin, wiggling back a tad bit to roll you onto your back, watching your face in the dim light of your shared bedroom. You squeak softly and look into his sockets as his tail slides under your damp underwear, rubbing small circles into your clit. You moan and wiggle in pleasure, panting softly as you look at him.

“Ooh, ya like that huh? Want m’ tail in ya~?” he teases, grinning wide as he pulls your panties down your legs and tosses them to the side of your nest, pulling a leg over him to keep them spread. You nod desperately and roll your hips against his tail. Your mate hisses softly, nuzzling into your neck as his tail slips between your folds, rubbing teasingly before pressing inside inch after teasing inch. 

The feeling is nearly indescribable, his smooth scales tucking tightly against himself so as not to scrape as he inched inside. The way it wiggles occasionally to make sure he’s not pinching anything only adding to the amazing feeling. He stops and watches your face, his own dark with orange as he runs his tongue over his teeth. You peek out of the corner of your eye at him, mewling at his lustful expression. He grins wider, gold fang glinting slightly in the light. 

“Oh, ya likin’ this more than I expected. Isn’t that right, Sugar~?” he coos, the hand not holding his head up sliding across your leg to ghost across your pussy. You shudder and squeak, rolling your hips into his hand and appendage inside you which pushes the tip of his thick tail against the special spot within you, ripping a louder, lewder squeak from your lips. Mutt hisses slightly as you squeak, leaning closer to you to whisper against your ear.

“Answer me, little mouse or i might just...give in n take a nice big bite a that pretty lil neck a yours~” he emphasises his words with a rough thrust of his tail and a suggestive bite at the area just below your ear. You squeak again, this time mixed with a whorish moan as you clench around him. How he knows about your little kink you’ll never know, but you love it-and him- so much that you don’t even care. “Y-yes! Please Mutt~” you whimper, arching your chest out to him and rolling your hips again, squeaking as he thrusts with your movement, tearing more squeaky moans out of your lungs. 

Your mate grins even wider and moves slightly to press his tail deeper into you, the tip wiggling and squirming inside as it tries to find the special spot. You shiver and mewl, arching your back into his touches as his hand travels back up to your tits to grope and rub them. His tail brushes lightly against the spot and you squeak loudly, sure the neighbors heard but not caring as your hips buck and jerk into him, moaning and mewling desperately as you feel yourself tighten around his tail. Mutt feels this and slides his tail out of you swiftly just as you’re about to cum, pulling with it needy and desperate whine. 

“Aww, what's wrong little mouse? Did ya think I'd let you have all th fun~?” he hisses, pulling your hips back against his, pressing his cocks against you but not yet putting them in. You mewl and try to grind down onto them but his clawed hands grip your hips tighter as he hisses dangerously into your ear, causing a shiver to roll down your spine. 

“Impatient are we? Look at you, ya soaked m tail n still want me ta fuck ya. Such a needy mouse, just begging to be played with~” he teases, rubbing his one of his cocks against your clit, pulling more whiny sounds from your form. You whine and mewl at him, begging as you rock and grind your hips against his dicks so close to being inside you it physically hurts. “P-please~ please M-mutt~!” 

He trills happily and wiggles your positions to where one arm is holding your leg aloft and the other is gripping your hip, slowly rocking his own back and forth to rub his dicks along your dripping core which drags a shiver laced with a mewl out of you. Your mate hisses at your eagerness and moves his hand from your leg to between them, grabbing his cocks and rubbing the tips against your slick entrance, earning a whining moan from your lips. 

You hear him suck in a sharp breath behind you and push both of his cocks inside you, making you gasp and whine, tensing up around his heads. Mutt feels you tense up and stops, humming soothingly. You’ve always loved his voice, even when you first met him you still couldn't help being soothed and lulled to sleep by his deep gravelly voice. You purr softly, trying to press your back into his chest but your bound arms are in the way. 

“Don’t worry, Sugar, i can make it feel reeeal nice~” he coos, licking on your neck before his fangs elongate slightly and pierce your skin. You squeal and whimper, legs shaking slightly as you drool slightly from the feeling of his teeth in your skin. He hums softly around your neck, a warm feeling spreading out from his bite, he’s injecting you with...something. You don’t care because it feels so damn good. Your body immediately relaxes enough for him to thrust both of his dicks inside you, making you mewl and shudder, not being this full before but loving every delicious inch of him inside you. 

He hisses softly around your skin, tongue flicking out to catch the small drops of blood that seep from around his fangs as he slowly thrusts into you. You moan loudly as your vision gets hazy and your mind goes foggy from the...whatever it was that Mutt just injected into your shoulder. “P-please...Sugarscales please i-i need you to fill me~” you mewl uncontrolled as you try to bounce on his cocks. He growls and moves his hand from his own parts to grip your hips better and thrust harder into you, his cocks pressing againt the sweet spots inside you. 

“Anything for you, my love…” he mumbles around your neck and adjusts your leg in his grip, thrusting deeper, harder and faster into you. You mewl and squeak loudly, tits bouncing with his thrusts as you twitch and convulse around him. With every throb of your cunt around him, more of the mysterious feel-good juice being pumped into your neck. 

Normally you’d be self conscious of how loud you are during your…”fun”, but something about this time is just so good that you lose all your doubts. You whine and mewl and moan loud enough for surely your whole surrounding neighbors hear, but you don’t care, as long as Mutt keep ramming himself into you, you couldn’t care less about anything outside of your nest.

You aren’t sure how long it takes for you to cum because time turns into a blur around you. Next thing you know, even more of the injected liquid ripples through you along with a long drawn out growl from Mutt as his cocks fill you with his cum, shooting deep inside of you. “A-aaaah Muuuuutt~” you whine, arching at the feeling of him filling you even more.

He makes a noise mixed between a hum and a hiss as he pulls his fangs out of your skin, turning your head to kiss you deeply, fangs still elongated and dripping the substance against your tongue. It tingles against your skin, making it slightly numb as you mewl into your mate’s mouth, him still thrusting into you deeply. You pull back slightly, tongue out, panting and drooling at how good you feel, at how amazing your mate made you feel. He releases your arms from his magic and pulls you back against him lovingly, letting you wiggle the feeling back into your limbs. 

“S-see? I told you that I’d be fine~” you coo, nuzzling into his chest. He grumbles happily and wraps his arms gently around your tummy as his tail coils protectively around the two of you. You lay there in silence for a while, lust listening to your rapid heartbeat calm to what it’s supposed to be. 

“So...what’d ya think a my venom? ‘S got some stuff in it ta make everythin’ feel good~” Mutt mumbles, nosing your back lovingly. You gasp softly, so that’s what it was! “W-well it fe-” you start but are interrupted by peaceful snoring from behind you. You roll your eyes and huff softly, oh well, you’ll talk to him in the morning about it. For now, the aftereffects of his venom making you extremely tired so you give in, letting the glorious feeling of sleep wash over you.


End file.
